1. Field of the Invention
The present invention relates to a figure displaying device such as visual scene display of the CGI (computer generated image) type, which displays figures on a Braun tube (cathode-ray tube) of the raster scanning type based upon the data prepared by an electronic computer or the like.
2. Description of the Prior Art
The figure displaying devices of this type employ a raster scan television as a monitor, and the screen on the Braun tube is successively scanned in the horizontal direction y and in the vertical direction t as shown in FIG. 1. Although most of the contents to be displayed consists of edges, it has been attempted in the past to color the displayed figures to display them as color images.
FIG. 2 schematically illustrates the formation of a figure displaying device of this type, which consists of a vector generator 1 made up of a digital differential analyzer (DDA) or the like, an edge-to-surface converter 2, a coloring circuit 3, and a TV monitor 4.
Upon receipt of the figure data from the computer, the vector generator 1 generates edges for every horizontal scanning period, i.e., generates y.sub.S.tau. and Y.sub.R.tau. in a horizontal scanning period t=.tau. as shown in FIG. 3, to form vectors AB, BC, AD and DC, i.e., to form edges of a figure ABCD in a 1-frame period. Edge data which is the result of the operation of the vector generator 1 is fed to the edge-to-surface converter 2 to convert the data into a surface pattern as indicated by P.sub..tau. in FIG. 3. The surface pattern is then colored by the coloring circuit 3 which generates a brightness signal. The brightness signal is then displayed on the monitor 4.
The edge-to-surface converter 2 employed by the above-mentioned figure displaying device contains a memory for storing the edge data generated by the vector generator 1, and a reading circuit for successively reading the contents stored in the memory.
To display the figures by the above-mentioned figure displaying device maintaining high resolution, however, the memory and reading circuit must be operated at high speeds. A limitation, however, is imposed on the operation speed. It is therefore difficult to markedly increase the resolution of the displayed figures.